The invention relates to a process for removing a cyclododecanone-rich fraction from a dehydrogenation mixture comprising low boilers, cyclododecanone, medium boilers, cyclododecanol and high boilers. In the following description, terms and addreviations as defined in the following paragraphs will be employed.
Butadiene is used hereinafter as a short name for the substance 1,3-butadiene (CAS No. 106-99-0).
CDT is used hereinafter as an abbreviation for 1,5,9-cyclododecatriene (CAS No. 4904-61-4).
CDEN is used hereinafter as an abbreviation for cyclododecene (CAS No. 1501-82-2).
CDAN is used hereinafter as an abbreviation for cyclododecane (CAS No. 294-62-2).
CDON is used hereinafter as an abbreviation for cyclododecanone (CAS No. 830-13-7).
CDOL is used hereinafter as an abbreviation for cyclododecanol (CAS No. 1724-39-6).
CDOL t.q. stands for CDOL in technical-grade quality and refers to a mixture containing 75 to 85% by weight of CDOL and 10 to 20% by weight of CDON.
Oxime is used hereinafter as a short name for the oxime of CDON (CAS No. 9466-89-4).
Laurolactam is a common name for azacyclotridecan-2-one (CAS No. 947-04-6).
Laurolactam is the starting material of the production of the high-performance polymer nylon-12. Laurolactam may be obtained on the industrial scale via the following route: butadiene, which is obtained in mineral oil processing, may be converted by catalytic cyclotrimerization to CDT. Hydrogenation of CDT gives CDAN. Oxidation of CDAN with (atmospheric) oxygen results in a mixture of CDOL and CDON. This mixture is subjected to a dehydrogenation which converts the CDOL present in the mixture to CDON. A dehydrogenation mixture comprising principally CDON is obtained. In addition, the dehydrogenation mixture comprises unconverted CDOL and further components. High-purity CDON is separated from the dehydrogenation mixture. The high-purity CDON is oximated to its oxime. The oxime may subsequently be reacted with sulphuric acid to give laurolactam.
The overall process is described in greater detail in Oenbrink, G. and Schiffer, T. 2009. Cyclododecanol, Cyclododecanone, and Laurolactam. Ullmann's Encyclopedia of Industrial Chemistry. DOI: 10.1002/14356007.a08_201.pub2.
The present invention addresses the problem of workup of the CDON/CDOL-containing dehydrogenation mixture with the aim to obtain high-purity CDON.
The dehydrogenation mixture obtained by the route described above comprises, as well as CDON and CDOL, further components in the form of low boilers, medium boilers and high boilers.
“Low boilers” in the context of this invention are substances or substance mixtures which have a lower boiling point than CDON under the same pressure conditions and are therefore enriched in the distillate in the course of distillative separation of a mixture of low boilers and CDON. The significant low boilers in this connection include: cyclododecene (CDEN), cyclododecane (CDAN), dodecanal, and cyclododecane epoxide. Cyclododecane epoxide is at the limit of the above definition of the low boilers, since its boiling point of about 150° C. at 40 mbar corresponds virtually to that of CDON and it is therefore virtually inseparable in an economically viable manner from the CDON. Smaller amounts (less than 100 ppm) of the low boilers acetic acid and decane may also be present, but these are barely of any relevance for the separation tasks.
“Medium boilers” in the context of this invention are substances or substance mixtures which, under the same pressure conditions, have a higher boiling point than CDON and a lower boiling point than CDOL, and are therefore enriched in the middle of the column in the course of distillative separation of a mixture of CDON, medium boilers and CDOL. A medium boiler in this connection is particularly dodecan-1-ol. The fraction of the medium boilers may include further organic substances which have not been fully characterized to date.
“High boilers” in the context of this invention are substances or substance mixtures which, under the same pressure conditions, have a higher boiling point than CDOL and therefore remain in the residue in the distillative separation of a mixture of high boilers and CDOL. The high boiler limit is at about 180° C. and a pressure of 46 mbar. The high boilers include especially cyclododecanediol. In addition, the fraction of the high boilers comprises further organic substances which have not been characterized specifically to date.
The dehydrogenation of CDOL to CDON is described in DE1568317 and DE1248650. These describe dehydrogenation mixtures containing 74 to 89% by weight of CDON and 25.9 to 21.8% by weight of CDOL. The remaining fraction of the dehydrogenation mixture prepared is accounted for by low boilers and medium boilers. The workup of the dehydrogenation mixture is not described any further.
Japanese patent application JP05-000977A discloses a process for preparing high-purity CDOL from a CDON/CDOL mixture. During the distillative workup of the mixture, a small proportion of alkaline components is added to the mixture to be separated. A dividing wall column is not utilized for workup of the mixture.
The oxidation of CDAN to an oxidation mixture comprising CDAN and CDOL is described in GB930842. The processing steps according to the present invention are not disclosed.
DE2031782 describes a process for selective preparation of CDON, in which CDAN is oxidized in order to obtain a mixture of CDON and CDOL. The mixture is worked up by distillation, but without more specific description of the distillation operation.
WO2009/092682 discloses a process for workup of a CDON/CDOL-containing mixture, which is worked up with the aid of a dividing wall column. In this process, however, the medium boiler is the main component of the feed, while the low and high boilers are unwanted by-products.
The processing of a laurolactam-containing mixture in a dividing wall column is mentioned in EP2336112A1. According to the process described, the feed to the dividing wall column consists predominantly of medium boilers.
The CDON used for the preparation of laurolactam should be present in a form of maximum purity, since accompanying components cause lasting damage to the polymers in the nylon-12. These secondary components arise particularly during the oxidation of the CDAN and also during the dehydrogenation of the CDOL.
Thus there remains a need for a process for the workup of a mixture comprising low boilers, CDON, medium boilers, CDOL and high boilers which yields CDON of maximum purity.